Subsurface valves are employed to perform a variety of services or tasks in the drilling, completion and production of oil and gas wells. In the performance of this work, it is frequently necessary to manipulate the valve from its open to its closed condition, or vice versa, while the valve is at its subsurface location. In opening or closing a valve carried by a tubular pipe string, a ball or pump down plug may be inserted into the string at the well surface and pumped down to the valve, where it creates a pressure increase to shift the valve from its closed to open condition, or vice versa. While this technique for change of the valve state is simple and effective, it is not easily employed where the pipe string contains a wire line or other internal obstruction. Moreover, the described system is usually limited in the number of times the valve condition may be changed without withdrawing and resetting the valve. Another technique for changing the valve state is to lower a wireline tool to the valve. This procedure is time-consuming and requires additional surface-operating equipment such as a wireline unit and a wireline lubricator.
One prior art system employs hydrostatic pressure changes in the fluid to shift the subsurface valve between open and closed positions. The prior art valve may be cycled several times by pressuring up and bleeding off the pressure of the fluid in the pipe string before having to be retrieved and reset.
Another prior art system, described in European Patent Application No. 90307273.4 (Publication No. 0409446A1) employs a flow-responsive shifting mechanism to alternately lock or release a subsurface tool. Monitoring the flowing fluid pressure provides a surface indication of the locked or unlocked status of the tool. Tool activation is accompanied by the application or reduction of forces acting through the pipe string supporting the tool. U.S. Pat. No. 4,491,187 describes a pressure-actuated downhole tool carded on a drill string that can be repeatedly cycled between expanded, intermediate and retracted positions by cycling the drill string pressure.
Prior art valves which are capable of remotely opening and closing the downhole valve using a ball or pump down plug to increase fluid pressure are limited in their uses and cannot be easily recycled between open and closed positions. Pressure activated downhole tools which may be repeatedly cycled are generally complex and expensive. Accordingly, well operators have generally sacrificed the advantage of repeated cycling of a downhole valve in favor of the high reliability and lower costs associated with valves which utilize a ball or pump down plug to create the pressure differential required to shift the downhole valve.
The disadvantages of the prior art are overcome by the present invention. An improved pressure-activated bypass valve and method of cycling a downhole valve are hereinafter disclosed. The valve and method of the present invention are particularly well suited for hydrocarbon recovery operations when high reliability is required.